How you have this listed the craft score reduces the cost...Why would a verditius with a high craft score charge less than one with a low craft score? They are able to make a better quality item more quickly.
So the price should be
Base Metal x Large = 5 x 3 = 15 Pawns to Open (reduced to 9 through
Argens's Craft skill so he gets a bit extra in payment)
4 Pawns for the linked-trigger
3 Pawns for the Unseen Opponent
Total = 22 Pawns
Ah, well, that ambiguity aside, I want to sell the device so any way I can lower the cost while still adhering to the strange house-mandated three-times build cost rule works in my favour. I could charge more but if the buyer decides to pull out over cost, then I don't get anything.
In any case, I'm not sure which way to go with this device now. I thought I had it cracked with the linked-effect version but the storyguide prefers the new version outlined above but I'm not sure whether it really covers all the bases.